Positioning control apparatus

ABSTRACT

A positioning control system for positioning a movable member includes a comparator for comparing a controlled variable with a command variable to provide an actuating or error signal. An electric controller provides an electrical manipulated variable signal from the actuating or error signal. A detector will detect when the actuating signal is smaller than a predetermined value to thereby cause the electric controller to change and thereby increase the lag characteristic thereof such that the movable member is quickly and accurately positioned.

Umted States Patent [191 1111 3,777,243 Taguchi et al. Dec. 4, 1973 [54]POSITIONING CONTROL APPARATUS 3,283,229 11/1966 Lindahl 318/621 X [75]Inventors: Nobuo Taguchi; Takehiko Ono, both 1 3:53;"; Of Tokyo, Japan3,555,391 1 1971 Younkin 318/621 x [73] Assignee: Tokyo ShibauraElectric Company,

Ltd. Kanagawa ken Japan Primary Examiner-B. Dobeck Att0rney-N0rmar1 F.Oblon et al. [22] Filed: Feb. 14, 1972 Appl. No.: 225,888

COMMAND DA CONVERTER POSITION SIGNAL [5 7 ABSTRACT A positioning controlsystem for positioning a movable member includes a comparator forcomparing a controlled variable with a command variable to provide anactuating or error signal. An electric controller provides an electricalmanipulated variable signal from the actuating or error signal. Adetector will detect when the actuating signal is smaller than apredetermined value to thereby cause the electric controller to changeand thereby increase the lag characteristic thereof such that themovable member is quickly and accurately positioned.

5 Claims, 4 Drawing Figures BACKGROUND OF THE INVENTION 1. Field Of TheInvention This invention generally relates to a positioning controlapparatus and more particularly to a positioning control apparatusadapted for providing quick and accurate positioning of an object ormovable member.

2. Description Of The Prior Art Certain machines,such,for example, as anindustrial manipulator or a robot, have movable members such as an armportion and the like. conventionally, these machines have employed anelectro-hydraulic actuating system for controlling the movable membersthereofln such machines, a need exists for the quick and accuratepositioning of the movable member over a long operating time. In anattempt to accomplish the above, particular consideration has been paidto the design of the electro-hydraulic system thereof. For example, inthe electro-hydraulic system, an accurate servo-valve is used forconverting an electric signal such as the magnitude of an electriccurrent into a mechanical signal such as the flow rate ofa hydraulicfluid. Moreover, the hydraulic fluid employed had good characteristicsagainst variation with temperature and the like. However, even with theabove, it wasfound impossible to completely eliminate the drift of thehydraulic system.- Thus, because of this drift, a certain disturbance orextraneous input would exist in the hydraulic system of the positioningsystem. Such a distrubance has been known to cause a steady-state errorin the accuracy of the positioning system.

On the other hand,from the point of view of economical efficiency,spacefactors and the like, it was desirable to use relatively smallservo-valves, actuators operated thereby, and the like, for driving therelatively large movable member of the machine in response to anelectrical signal. However, in positioning systems having anelectro-hydraulic system wherein relatively small servo-valves andactuators are employed, it was impossible for the same to have a highgain. Moreover, by using relatively small components,there was atendency to decrease the accuracy and to increase the time constant ofthe electro-hydraulic system.

Typically, the overall positioning system would include a comparator fordeveloping an actuating or error signal from the command variable andthe controlled variable which was compared therewith, an electriccontroller for developing an electric manipulated variable from theactuating signal, an electrohydraulic servo-mechanism, and the object ormovable member to be controlled by the servo-mechanism. In order toaccurately effect the positioning control, it was necessary to make theloop gain in the overallpositioning system as high as possible, yetmaintain the stability thereof. As described above, the gain of theelectrohydraulic system was of a relatively low value so that the gainof the electric controller had to be high. However, by providing anelectric controller having a substantially high gain, the stability ofthe overall positioning system would be adversely affected and actuallyreduced. Additionally, a lag or integral characteristic was usuallyprovided in the electric controller to thereby substantially reduce thesteady-state error which was chiefly caused by the extraneous input,such as the drift of the electro-hydraulic system. However, such anarrangement which provided the controller with anintegrating operationwould often result in there arising a relatively large lag of phase.This was particularly a problem at relatively low frequency ranges.Also, a relatively large overshoot in the movable member beingcontrolled would occur. Such a lag of phase would result in a decreasein the speed of the positioning control apparatus, while the overshootwould result in a decrease in the accuracy of positioning.

SUMMARY OF THE INVENTION Accordingly, it is an object of the presentinvention to provide a new and improved unique positioning controlapparatus which is capable of quickly and accurately positioning amovable member.

It is another object of the present invention to provide a new andimproved unique positioning control apparatus which is stable and has arelatively small overshoot.

One other object of the present invention is to provide a new andimproved positioning control apparatus which includes an electriccontroller which is capable of changing the lag characteristic thereofat appropriate times.

Briefly, in accordance with the present invention, the foregoing andother objects are, in one aspect, attained by the provision of acomparator means for comparing a controlled variable with a commandvariable to produce an actuating or error signal and an electriccontroller for developing a manipulated variable from the actuating orerror signal. Additionally, an electrichydraulic means is provided fordriving the movable member in response to the manipulated variable and adetecting means is provided for detecting when the actuating signal issmaller than a predetermined value to thereby cause the electriccontroller to increase the lag characteristic thereof.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be morefully understood from the following description when taken in connec-DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to theDrawings, wherein like reference numerals designate identical orcorresponding parts throughout the several views, and more particularlyto FIG. 1 thereof, wherein one preferred embodiment of a positioningcontrol apparatus according to this invention is shown with an object ormovable member to be positioned being indicated by a reference numeral10.

An analogue signal corresponding to the position of the object ormovable member 10 which may either be electrical or mechanical, isapplied to a detector 11 which produces a digital position signalcorresponding thereto. The digital position signal from the detector 11represents a controlled variable and is fed back to a reversible counter12.

The counter 12 is adapted to count up a command variable or instructionpulse train to the contents thereof and to count down the positionpulses generated by the detector 1 1. In accordance therewith, a signalhaving a magnitude which is equal to the difference between the commandposition and the actual position of the object or movable member 10 isprovided in digital representation as an actuating or error signal A 2 A2 A 2 A,,2". The digit lines A to A,, at the output of the counter 12are connected to corresponding input terminals of a digital-to-analogueconverter 13. A sign signal S is also applied from the counter 12 to thedigital-to-analogue converter 13. An analogue actuating or error signalincluding a sign component is therby obtained at the output terminal ofthe converter 13. An amplifying device 14 having an input resistor l5,anamplifier l6 and a feedback resistor 17 is provided for amplifying theactuating or error output signal of the converter 13. The signal soamplified is then applied to an operational amplifying device 18 whichincludes an input register 19, a high gain amplifier 20, and a feedbackelement generally shown at 21. The feedback element 21 has a resistor22, a condenser 23 which is serially connected to the resistor 22, and anormally open contact 24 which is connected in parallel 'with thecondenser 23. The contact 24 is actuated by a relay 25 as will beexplained in detail hereinafter.

The output of the operational amplifying device 18 is further amplifiedby a power amplifier 26 and is then applied to an electro-hydraulicservo-system 27 which includes a servo-valve and an actuator not shown.The servo-valve converts the output signal of the operational amplifier18 into a corresponding flow rate of the hydraulic fluid supplied from ahydraulic fluid source 28. The hydraulic fluid thereby operates theactuator which, in turn, drives the object or movable member 10.

In order to detect when the magnitude of the positioning error is higherthan that corresponding to a selected and desired value, such as threeincrements of the digital representation, an OR-gate 29 is provided andis arranged to receive at the input terminals thereof the signalsappearing on the digit lines A to A The output of the OR-gate 29 isamplified by an amplifier 30 and is then supplied to the relay 25. Thus,when at least one of the inputs of the OR-gate 29 is of a high value,the same will produce a high output which is amplified by the amplifier30 to cause relay 25 to operate. Accordingly, the relay 25 will operateso as to close the contact 24 during that period of time when thepositioning error is of a value larger than that corresponding to threeincrements.

In operation, when a command such, for example, as 100 positiveincrements (this may mean, for example, a movement of the object ormovable member l0 by cm. in a forward direction if one incrementcorresponds to 1 mm.) is applied to the counter 12, the OR- gate 29 willproduce a high output to cause the relay to operate whereby the contact24 thereof is closed. The closing of the contact 24 will short-circuitthe condenser 23 and thereby remove any lag or integral characteristicof the operational amplifier 18. Accordingly, the object or movablemember 10 to be positioned will be moved toward the desired targetposition in a manner having a much smaller controlling lag than that ofthe case where "the operational amplifier has a lag characteristic. Thatis, the object or movable member 10 can be moved toward the targetposition with a relatively high speed.

Now, when the positioning error reaches to within three increments, theOR-gate 29 will stop generating a high output therefrom so that therelay 25 will be deenergized and thereby cause the contact 24 thereof toopen. The condenser 23 will then be inserted into the feedback loop ofthe amplifier 20 whereby the operational amplifying device 18 will nowhave a lag characteristic. It should be understood that up until thistime, the condenser 23 had no charge, since the same has been shunted orshort-circuited by the contact 24. Thus, a smooth transfer or changeoveroperation from a first mode wherein the condenser 23 is removed to asecond mode wherein the condenser 23 is inserted is obtained. In thesecond mode of operation, the object or movable member 10 is moved tothe desired command position. Now, if it is realized that the transferfrom the first mode of operation to the second mode of operation isperformed in the vicinity of the target position, then it will beapparent that the characteristic of a smooth transfer serves to enableboth a smooth and stable positioning of the object or movable member 10.The above described operation is illustrated in FIG. 2a.

In the second mode of operation, the controlling lag will not affect thepositioning operation, since the second mode of operation is employedonly in the vicinity of the target position. With regard to overshoot,the amount of the same is substantially negligible with the presentinvention, since the amount of overshoot generally depends on thecharacteristics of the system and the second mode of operation isemployed only in the region of a small error signal. If the wholeoperation is performed by the second mode of operation, the object ormovable member 10 to be positioned will be controlled as shown by thedotted line in FIG. 2bfThe above discussion will be easily understood bycomparing FIGS. 2a and 2b.

If the whole operation is performed by the first mode of operation, theobject or movable member 10 to be positioned will be controlled as shownby the solid line in FIG. 2b. However, since a steady-state errorusually occurs as a result of an extraneous input, such as the drift ofthe electro-hydraulic actuating system, it is noted that the second modeof operation must be employed in the region where the steady-state errormay occur. In other words, the detecting means for controlling the relay25 must be adjusted to satisfy the above requirement.

Referring now to FIG. 3, another preferred embodiment of this inventionis shown as including an analogue comparator 31, an error detector 32for producing an output when the error or actuating signal is largerthan a predetermined value, and a position detector 33. The otherportions of the embodiment of FIG. 3 are substantially the same as thatshown in FIG. 1. In this embodiment, the command variable is supplied inthe form of analogue signal. The error detector 32 may be constructed byusing a Schmidt triggering circuit or the like.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. For example, anelectronic switch may be readily used in place of the contact 24. It istherefore to be understood that within the scope of the appended claims,the invention may be practiced otherwise than as specifically describedherein. What is claimed as new and desired to be secured by LettersPatent of the United States is:

1. A positioning control system for positioning a movable membercomprising:

comparator means for comparing a controlled variable with a commandvariable to produce an actuating signal; an electric controller fordeveloping a manipulated variable in electrical representation from saidactuating signal, said electric controller being able to increase a lagcharacteristic thereof; electro-hydraulic means for driving said movablemember in response to said manipulated variable; and detecting means ina forward signal path for detecting when said actuating signal issmaller than a predetermined value to thereby cause said electriccontroller to increase said lag characteristic thereof.

2. A positioning control system according to claim 1, wherein saidpredetermined value is equal to or larger than a maximum value of anysteady-state error which may occur.

3. A positioning control system according to claim 1, wherein saidcomparator comprises a reversible counter and a digital-to-analogueconverter, and said detecting means detects a digital representation ofsaid actuating signal from said counter.

4. A positioning control system according to claim 1, wherein saidelectric controller comprises an operational amplifier.

5. A positioning control system according to claim 4, wherein saidoperational amplifier comprises a feedback loop including a resistor anda condenser serially connected thereto, said condenser being arrangedsuch as to be capable of being shunted in response to the operation ofsaid detecting means.

1. A positioning control system for positioning a movable membercomprising: comparator means for comparing a controlled variable with acommand variable to produce an actuating signal; an electric controllerfor developing a manipulated variable in electrical representation fromsaid actuating signal, said electric controller being able to increase alag characteristic thereof; electro-hydraulic means for driving saidmovable member in response to said manipulated variable; and detectingmeans in a forward signal path for detecting when said actuating signalis smaller than a predetermined value to thereby cause said electriccontroller to increase said lag characteristic thereof.
 2. A positioningcontrol system according to claim 1, wherein said predetermined value isequal to or larger than a maximum value of any steady-state error whichmay occur.
 3. A positioning control system according to claim 1, whereinsaid comparator comprises a reversible counter and a digital-to-analoguecOnverter, and said detecting means detects a digital representation ofsaid actuating signal from said counter.
 4. A positioning control systemaccording to claim 1, wherein said electric controller comprises anoperational amplifier.
 5. A positioning control system according toclaim 4, wherein said operational amplifier comprises a feedback loopincluding a resistor and a condenser serially connected thereto, saidcondenser being arranged such as to be capable of being shunted inresponse to the operation of said detecting means.